Size and Weight
The chiru stands 83 - 100 cm at the shoulder. Females weigh about 26 kg; males weigh about 40 kg. It is fawn to reddish brown in color on the back, and beige or offwhite on the underside. Adult males have a striking black face, black markings on the legs, and long, lyre shaped horns used to defend their harems. Females do not have horns.
Age to Maturity
As with many medium-sized ungulates, female chirus probably first conceive at the age of 1.5 or 2.5 years and give birth at the age of 2 or 3 years.
Gestation Period
7 - 8 months
Birth Season
Female chirus give birth in the second half of June and early July. The approximate main mating season is in late November and December.
Birth Rate
Females give birth to a single young.
Maximum Age
At least about 8 years (wild).
Dispersal
Sometime in late April or May, most 10- to 11-month old males separate from their mothers and either join their male peers or associate with adult males until early winter, when, like the adult males, many join mixed herds. Young females remain with their mothers.
Diet
The chiru is a grazer and perhaps a browser (Nowak 1999). It feeds mainly on forbs, grasses, and sedges.
Behavior
Movement patterns of the chiru are complex, and the movements of the two sexes must be discussed separately. Males and females are mostly on the same winter grounds during the rut.
During spring, some females remain on the winter grounds in resident populations, but others migrate. In May and June the migratory females and their female offspring separate from the males and travel up to 300 km (190 mi) north into desolate and uninhabited terrain to summer calving grounds. They migrate back to the fall and winter grounds in late July and early August.
Males have several movement patterns. At some point in late April or May, most 10- to 11-month old males separate from their mothers and either join their male peers or the adult males, which also part from the females at that time. Some males remain on the winter grounds as resident populations. Many males travel at least a short distance to a summer range. Some males travel far from their winter grounds, usually northward, dispersing widely, and then in autumn return to traditional fall and winter grounds for the rut. As a result of these diverse movement patterns, males, in contrast to females, tend to be scattered throughout the range of the species during summer.
Age and Gender Distribution
Between 1990 and 1993, the combined central and eastern populations in the Chang Tang region of Tibet averaged 29 percent males, 53 percent females, and 18 percent young. Under normal circumstances the ratio of young to females ranged from about 30:100 to 50:100.
Mortality and Survival
Schaller concluded that mortality of young was high, up to half dying within a month or two after birth, and that at least 2/3 of the chirus died between birth and the age of 2 years.
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